I like Universal Nutrition's products in general and N1-T, Natural Testosterone Supplement is no exception. The formula seems thoughtfully designed, though I'm suspicious that the average user can expect "to nearly double testosterone", as the manufacturer claims. Tribulus (protodioscin) does mimic Luteinizing hormone (LH), which in turn stimulates Leydig cell production of testosterone in the testes. However, indipendent clinical trials of Tribulus and its effects on human testosterone have shown mixed results. Other (probably) effective ingredients include avena (avenacosides A & B) and "patented longjack (Eurypeptides)", though it's beyond me what "patented" longjack means. While I like this product, I give it four stars and not five because, to me, the price is a bit too high, and I'd also like to see a few other ingredients added to this formula, like Maca or Mucuna pruriens.